Acute Pancreatitis is potentially lethal when severe and is increasing in incidence, resulting in significant health care burden and costs. Obesity is associated with severe AP. Mortality from AP after the first week results from severe pancreatic necrosis and its associated complications, allowing a therapeutic window period. However, care currently consists of conservative management and treatment of its complications. Severe pancreatic necrosis in humans occurs with fat necrosis, which results from the saponification of free fatty acids along with elevated adipokines. Whether these are an epiphenomenon or causal in the disease is unknown. PRELIMINARY DATA: To study this obesity-associated exacerbation of AP, we examined pancreas histology from autopsies of controls and patients with pancreatitis. We noted an increase in the amount of intrapancreatic fat (IPF) with BMI in both groups. In AP patients, there was significantly more fat necrosis compared with controls, which was accompanied by surrounding acinar necrosis, which decreased with increasing distance from the fat necrosis. This peri-fat acinar necrosis contributed to about half of the total acinar necrosis. In contrast, IPF in patients with chronic pancreatitis seemed unrelated to BMI, was accompanied by fibrosis, which walled off fat necrosis, limiting peri-fat acinar damage. To understand this mechanistically, we generated a novel acinar-adipocyte co-culture system. While acini and adipocytes functioned normally in this medium both individually and together in the presence of the lipase inhibitor orlistat, omission of orlistat resulted in near total acinar necrosis, as evidenced by propidium iodide uptake, drop in ATP levels, and absence of LC3-II increase. This was accompanied by a large increase in fatty acids and glycerol in the medium, with levels equivalent to those in aspirates from severe pancreatic necrosis in humans. Orlistat in the medium prevented acinar death and lipolysis and restored responsiveness of repurified acini to stimuli similar to control acini. Individually, unsaturated but not saturated fatty acids at levels present in aspirates from patients with severe pancreatic necrosis increased acinar cytosolic calcium and caused cytochrome C leakage and cell death. We therefore hypothesize that obesity-associated intrapancreatic fat worsens pancreatic injury via unsaturated fatty acids generated from local lipolysis. We propose to study the relative contribution of fatty acids and adipokines to acinar injury and inflammation. We additionally propose to identify the lipase(s) responsible for acinar injury. We will also compare the relevance of obesity to isolated IPF with and without fibrosis with regard to its impact on the severity of AP. These studies could open a new therapeutic frontier for this devastating disease by targeting specific lipases(s) and by stratifying patients according to risk of severe AP based on findings of IPF on imaging studies.